The aims of this protocol are to evaluate the cause and treatment of hypokalemia in patients who maintain this problem without an obvious cause and to characterize the renal handling of sodium, potassium, magnesium and calcium in relatives of patients with genetically confirmed Gitelman's or Bartter's Syndrome. Specifically, we would like to test the hypothesis that heterozygote relatives for Gitelman's or Bartter's mutations are more susceptible to diuretic-induced hypokalemia. We are also evaluating bone tunnover/bone density in all these individuals. To date, we have enrolled 16 family members on the in-patient side (10 heterozygotes and 6 family controls). For laboratory and genetic testing, we have recruited 117 members of an extended family with 26 members affected with Gitelman's syndrome.